Add a test.
Merge pull request #294 from bangerth/add-test

Add a test.
Reorganize code in symmetric_tensor.h.

The current implementation of SymmetricTensor<rank,dim,Number>::unrolled_to_component_indices
and its inverse function was only implemented for rank=2 and looked essentially like this:

  Assert (rank == 2, ExcNotImplemented());
  Assert (i < n_independent_components, ExcIndexRange(i, 0, n_independent_components));
  switch (dim)
    {
    case 1:
      return TableIndices<2>(0,0);
    ...

Such code cannot be generalized to rank=4 (in fact, it doesn't even compile
for rank=4) because we would have to return objects of different types
in any switch on rank. The only way around this is to use dispatch to
different functions that do the work for a particular rank.

This patch does the first part of this: set up the dispatch. Later patches
may in fact implement this function and its inverse for other ranks than 2.
Merge pull request #295 from bangerth/code-reorg

Reorganize code in symmetric_tensor.h.
Elide default initialization.

Apparently, the initialization of a std::shared_ptr with NULL is not
allowed with the Intel compiler. It is also not necessary (that's what
the default constructor does anyway), so just remove the line.
Merge pull request #296 from bangerth/fix-slepc-icc-problem

Elide default initialization.
CMake: Correctly detect -Wno-... support for gcc

gcc does not emit a warning if an unknown -Wno-... flag is specified on the
command line, thus the ENABLE_IF_SUPPORTED macro unconditionally enabled
-Wno-... flags for gcc. Unfortunately, gcc _does_ emit a warning for the
unrecognized compiler option if another warning is emitted in the same
compilation unit. This is now fixed by always querying for the non-negated
version, i.e. -Wfoo instead of -Wno-foo.
Merge pull request #297 from tamiko/fix_wno-xxx_detection_for_gcc

CMake: Correctly detect -Wno-... support for gcc